1. Field of the Invention
The present invention relates to a cooling system for an internal combustion engine for the purpose of reducing its fuel consumption and improving its exhaust gas characteristics and running performance.
2. Description of the Prior Art
Cooling systems of this kind have been known, for example, as shown in FIG. 1. With such a cooling system, when engine cooling water temperature is lower than a predetermined value, a thermostat 1 closes a passage to a radiator 5, so that water delivered from a water pump 2 flows through a cylinder block 3 and a cylinder head 4 and then returns to an inlet 7 of the water pump 2 through a bypath 6 as shown by arrows in FIG. 1 without entering the radiator 5. In other words in more detail referring to FIG. 2 which is an enlarged partial sectional view, the cooling water from the cylinder head 4 flows through the bypath 6 into the inlet 7 of the water pump and is then forced through an outlet 8 of the pump into an inlet 9 of a water jacket.
With such a conventional cooling device, however, the water is forcedly circulated through an engine by the operative water pump 2 even if the engine cooling water temperature is still low, so that the heat generated from the engine is unduly dissipated by the circulation of the water to delay the rising of the engine temperature. Such a delay of the rising of the engine temperature may adversely affect the fuel consumption, exhaust gas characteristics and running performance of the engine.